Liverpool midfielder Naby Keita was taken to hospital after being carried off with a back injury in the 1-0 Champions League defeat by Napoli.
Keita, who joined from RB Leipzig for £48m this summer, was taken off on a stretcher after just 19 minutes.
He received treatment on the pitch in Italy before being substituted.
Keita “underwent a number of precautionary health checks” to assess his condition, according to the club’s official website.
No decision has yet been taken on when the 23-year-old will be discharged.
Keita has made nine appearances for Liverpool this season, including four starts in the Premier League.